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lkm



Number of posts : 482
Registration date : 2008-05-05

PostSubject: Re: Airships   12.10.08 17:35

In size and shape this is very similar to what one would imagine a proper spaceship should look like. Put a reactor and some radiators on board and you could have a 400m VASIMIR sending you to Mars. Modify the ram scoop to a Bussard ramscoop and some of your remass could be the solar wind.
Alternatively, I'm sure it could launch a lot of missiles from a great height at high speed.
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davamanra



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PostSubject: Re: Airships   12.10.08 22:40

If a CSCS is ever built, one of the greatest assets would be a brain trust to develop these kind of ideas.
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lkm



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PostSubject: Re: Airships   13.10.08 7:05

In that case, how about another one. The airship elevated train system. Airship train carriages travel along electrified guide cables strung between 300m pylons. because the vast majority of the airship weight is never transfered to the infrastucture its construction can be relatively light and draw heavilly from existing electricity pylon design. Because the carriages never have to control their own direction or carry their own fuel mass can be saved to reduce the gas per passenger, as the airship will be designed to maintain a neutral bouyancy at 300m from the ground it can have drastically reduced altitude control systems saving massively on volume, especially as ballast can easiliy be added or subtracted at each station to match the number of passengers aboard and the ground elevation. Because they will be a near silent system requiring only infrequent construction of pylons construction will not be so objectionable to so many people. Airship train stations that look like they're from the jetsons will be massively cool.
Lastly, airship trains may represent an efficient application of maglev technology, without the requirement of levitating an entire train a linear motor system with magnetic guide rails only to keep it in line may make for a lower power less hardware intensive, economical system.
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davamanra



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PostSubject: Re: Airships   13.10.08 23:08

I like it. A major advantage would be that unlike trains you could build this system over any terrain. There wouldn't be any need to build bridges or tunnels or level terrain, just build taller or shorter pylons as necessary, which would make infrastucture costs compared to trains dramatically cheaper. Also you wouldn't have to worry about some idiot breaking down on the tracks!!
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BrianSlee



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PostSubject: Better   15.10.08 20:44

lkm wrote:
In that case, how about another one. The airship elevated train system. Airship train carriages travel along electrified guide cables strung between 300m pylons. because the vast majority of the airship weight is never transfered to the infrastucture its construction can be relatively light and draw heavilly from existing electricity pylon design. Because the carriages never have to control their own direction or carry their own fuel mass can be saved to reduce the gas per passenger, as the airship will be designed to maintain a neutral bouyancy at 300m from the ground it can have drastically reduced altitude control systems saving massively on volume, especially as ballast can easiliy be added or subtracted at each station to match the number of passengers aboard and the ground elevation. Because they will be a near silent system requiring only infrequent construction of pylons construction will not be so objectionable to so many people. Airship train stations that look like they're from the jetsons will be massively cool.
Lastly, airship trains may represent an efficient application of maglev technology, without the requirement of levitating an entire train a linear motor system with magnetic guide rails only to keep it in line may make for a lower power less hardware intensive, economical system.

I think you might be better served by a very light rail system. Composite cars on aluminum frames using elevated rails. Combine that with short range electric vehicles for local traffic.
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Locksley



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PostSubject: Re: Airships   15.10.08 21:47

Welcome to the board, Brian!

Speaking of electric vehicles, be sure you check out the transportation section if you haven't already.

In regards to AiRail, or whatever we want to call it, I can't imagine it being very fast. Quick point-to-point transportation would still need to be by high-speed train. However, applying it for light to heavy cargo transportation, I foresee a dramatic decrease in shipping costs. It could also be used for sight-seeing or guided trips through the city.
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lkm



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PostSubject: Re: Airships   16.10.08 3:37

In thinking up AirRail I was trying to address a very real if absurd problem in the western world, the near impossibility of getting anything important or large built without facing ten years of proffessional objectors. My thinking was that if AirCarriages were used then the structures required to be built to support the rail guides could be a lot lighter, fewer in number, and a whole lot taller. This would therefore require a minimum of ground footprint to be built upon, be it in a city or the country, and a at a height far above any existing structures. Thus I was hoping it would be much easier to get built than a conventional light railway would.
As for speed, I have no idea. Traditionally Airships max out around a hundred mph but a train of them would have very different power to drag so I'm not really sure what's possible.
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davamanra



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PostSubject: Re: Airships   16.10.08 6:48

This would be a good concept to experiment with for a cross country transportation system. Maybe start off with a intercity route of around a hundred miles. The infrastructure would be very minimal and this would be the way to get the bugs worked out of it. From there you just start expanding adding more cities to the route until you have crossed the country, the same way they did with the intercontinental railroads.
As for speed, the drag of an airship would be significant but even a hundred miles an hour is still faster than trains and since you could take a much more direct route, a hundred miles an hour in an airship would probably be comparable to 135 mph on a train.
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NoMoreLies



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PostSubject: Re: Airships   18.10.08 5:02

Perhaps a new thread should be created for the AirRail? Or maybe even a subforum for transportation in the CSCS.

I like the idea of a VTOL HTA Blimp, with ducted fans for hovering.
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lkm



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PostSubject: Re: Airships   18.10.08 13:30

I think, again, I suggested something similar in the CS cars thread. Say, 3m by 12m by 2.5m ovoid gas bag with a downward ducted fan at each corner and switchblade wings on top. Cabin at the front, engines at the rear, aerodynamic hard body shell all over. It should look something like those small shuttle craft on Firefly.
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NoMoreLies



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PostSubject: Re: Airships   19.10.08 7:09

I'd go with more of a flying wing shape, like the Black Triangles.
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davamanra



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PostSubject: Re: Airships   19.10.08 23:52

The ovoid shape would be very efficient volume-wise, but if a tail were attached to make it teardrop shaped it would be very aerodynamic.
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BrianSlee



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PostSubject: FYI   22.10.08 6:01

davamanra wrote:
The ovoid shape would be very efficient volume-wise, but if a tail were attached to make it teardrop shaped it would be very aerodynamic.

http://www.aerosml.com/ml866/
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davamanra



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PostSubject: Re: Airships   22.10.08 8:01

Ok so they stole their idea from Thunderbird 2, what's your point? LOL! When you described ovoid I was visualizing an egg shape, but this squat egg shape would be more aerodynamic. Still, a teardrop tail with flight controls attached would be even more aerodynamic as well as more maneuverable. You could even attach a ducted fan to the back that could provide thrust as well as maneuverability.
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lkm



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PostSubject: Re: Airships   22.10.08 8:54

Well it all comes down to volumetric efficiency, doesn't it? So either you consider an optimized lifting body of some sort or you stick on some wings. Personally, I came to the conclusion that given a craft with only a slight negative buoyancy the engineering of a pair of roof mounted swing wings would be comparatively simple and light weight making for a smaller more compact main body.
My design constraints were that it should minimise it's ground footprint and ideally be not much bigger than a minibus and able to nerge with conventional traffic. It should be HTA and VTOL, and capable of carrying a maximum of three people.
To clarify the design idea I layed out, athough I came up with several, I was envisioning an ellipsoid gas bag 12 metres long by 3 mtres wide by 2.5 metres tall which would provide arround 3.7 mt of lift when filled with helium. This would be encased in an aerodynamic body shell with a three seater cabin directly in front of the gas bag, ducted fans at each corner of the ellipsoid and, as you pointed out, a slight tapered tail with twin fans and flight control surfaces at the rear. Up top a pair of light weight wings are housed in an streamlined shroud and underneath there's a slight dihedral to the surface such that on low power the craft can operate like an inefficient hovercraft and manouver on the ground. Something like that.
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davamanra



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PostSubject: Re: Airships   23.10.08 8:07

I like your basic design, but there's still a lot of drag that is created by not having the air flow smoothly off the back. A lightweight tail, possibly made bouyant with a little helium to allow the air to flow smoothly would accomplish this. This would have no effect on the volumetric efficiency since it would be a separate compartment. It would be used solely as an aerodynamic feature.
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lkm



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PostSubject: Re: Airships   23.10.08 9:31

At this point I think only some wind tunnel testing would be able to effectively answer this question, all I can say is that weight wise maintaining a centre of gravity at a mid point between the lift fans might be fairly important and the aft section would be conterbalancing the cabin, adding more mass or aymetric lift might make things complicated, or simpler. I don't know. If a tail is neede, add a tail, aptera's cetainly look good with one.
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NoMoreLies



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PostSubject: Re: Airships   25.10.08 9:12

So, an ellipsoid with movable wings?

Why not fill it with Hydrogen? And don't post a picture of the Hindenburg, that was a lesson in why not to coat your blimp with thermite.

Say a human weights on average 100kg, surely 0.5mt would be enough? Even with Heliums 800g lift per cubic metre, that gives us 400kg if we fit in 500 cubic metres. Fit on some ducted fans and wings and we're set.
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lkm



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PostSubject: Re: Airships   25.10.08 10:02

I worked it out for hellium because it's the safe conventional choice and the numbers are easy enough to guesstimate in my head, 1g/L lift lends itself to that sort of thing. I have absolutely no problem with switching to hydrogen both for logistical reasons and to shrink the desing, the smaller the better.
An Skyship 600 weighs 5.5mt, an Aptera Typ-1 comes in at 0.67mt, I have no concrete idea how much this thing would mass but suspect it to be somewhere between these two figures. The 600 is about 5 times larger than what I proposed but I would think mass would not come down quite so linearly, the Typ-1 is much closer in design and construction to what is desired but I'm not sure how it would scale up. aiming for 4mt was just a conservative estimate, You could well build it for half that.
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davamanra



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PostSubject: Re: Airships   29.10.08 19:10

I was wondering about a "double hulled" design, where you had helium between the inner and outer layers to act as a barrier as well as a flame retardant and the interior filled with hydrogen. Granted, without doping there wouldn't be the Hindenburg type of burning but hydrogen can still burn with the right circumstances. This design would minimize the possibility of hydrogen combustion, but still give you the benefit of hydrogen's bouyancy
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lkm



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PostSubject: Re: Airships   30.10.08 7:13

As i understand it, part of the issue with hydrogen is that it has a high rate of molecular diffussion through solids, i.e it leaks. A double hull would thus slowly accumalate hydrogen in bubbles at the top of the helium cells, which would then diffuse upward so that the leaked hydrogen would then gather at the very top of the bag. I suppose it may be possible to devise some method to siphon the hydrogen bubbles off the top of each helium cell and back into the hydrogen bag but that could add a weight penalty. It might pay to consider, given the trouble of having to source both hydrogen and helium, instead having a very thin nitrogen shell as your double hull. Assuming you can easily design your thin hull cells with a peak to gather the leaked hydrogen and send it back to the main bag, nitrogen may be a better choice given it is far cheaper, just as inert, has a much lower diffusion rate than helium and is slightly less dense than air.
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NoMoreLies



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PostSubject: Re: Airships   30.10.08 8:52

Just ionise the Hydrogen and use an Electrostatic membrane to prevent leakage.
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lkm



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PostSubject: Re: Airships   30.10.08 11:24

That sounds dangerous.
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NoMoreLies



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PostSubject: Re: Airships   30.10.08 11:50

Not really. I'm not suggesting Ionising it all the way to a Plasma, I'm suggesting making it into a bag full of H- atoms, Ionised with an electron gun.
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lkm



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PostSubject: Re: Airships   30.10.08 18:22

Still, I think it might be safer to do that with Helium, especiallly as it's much more suceptable to electric fields.
Secondly, what do you think of heating the helium for extra lift? It's not something you could do with hydrogen but helium is so inert you could easily exceed hydrogen's lift capacity.
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NoMoreLies



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PostSubject: Re: Airships   02.11.08 7:36

How far can we heat it? Say we make it 50% less dense, that would be reaching 1kg/m3
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lkm



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PostSubject: Re: Airships   10.11.08 17:33

Don't hold me to this, but I think if you heat it to 500K or so you halve the density of helium. Of course you then have to start thinking about materials, and insulation, maybe a thin shell of aluminium covered by aerogel and then a composite shell, but it all adds weight. A further thought is that you can do much the same by halving the internal pressure and having a stronger shell, which with modern composites might be possible, wiht the added benefit of slowing disfusion. It may be that best compromise between energy mass and lift is a combination of a lower pressure and a hotter gas.
Finally either of thes ideas is going to require air bladders of some form.
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